The present invention relates to an adjustable steam-flow control arrangement for an electric steam iron and, more particularly, to a steam flow control arrangement that provides precise and repeatable control of the steam flow in an electric steam iron.
Conventional electric steam irons include a steam generation circuit by which water in a reservoir is supplied to a steam generator with the steam directed to the fabric to be ironed. Most steam generation circuits include a metering valve by which the water flows from the reservoir in a drip-wise manner onto a heated surface, such as the soleplate, and is flashed to steam. The metering valve typically includes a small-diameter orifice between the water reservoir and the steam chamber with the distal end of a metering rod extending into the orifice. The distal end of the metering rod has a variable cross section so that the water flow rate can be controlled by extending the distal end into or withdrawing it from the orifice.
Various mechanical arrangements have been employed to control the position of the metering rod relative to the orifice with cam control being the most common. Typically, the electric iron is provided with a steam-flow control knob that is rotatable about an axis and which includes or is connected to a helical cam surface. The cam surface can include detent positions so that the user can select predefined "low," "medium," and "high" steam generation rates and can include an "off" position for dry ironing. The upper end of the metering rod is configured to engage the cam surface so that rotation of the steam control knob by the user in one direction will withdraw the other end of the metering rod from the orifice to increase the water flow to the steam chamber and rotation of the control knob in the other direction will extend the other end of the metering rod into the orifice to decrease the water flow to the steam chamber. The control arrangement is such that the metering rod can also seal the orifice to stop the water flow and the generation of steam to allow dry ironing. While cam control systems have enjoyed widespread use in the steam iron art, the cam-control system lacks a certain precision in its operation since dimensional clearances can accumulate so that it is often difficult to provide small increments or decrements in the steam flow.
Another type of steam control arrangement having a higher degree of control is the threaded-mount arrangement in which the metering rod is mounted in a threaded bushing in the body of the iron. A user-operable steam control knob is secured to the upper end of the metering rod and is rotatable by the user in one direction to withdraw the other end of the metering rod from the orifice to increase the water flow to the steam chamber and rotatable in the other end direction to insert the other end of the metering rod into the orifice to decrease the water flow to the steam chamber. Since the pitch of the screw threads can be specified at the design stage, precise and repeatable control can be obtained. However, the threaded mount arrangement, in contrast to the cam-control system, requires several rotations of the steam control knob to effect control throughout its full range of operation. Accordingly, it can be difficult to select a desired steam flow rate position.